Many vehicles such as a combines construction back hoes, road pavers, vibratory drum rollers, etc., are quite often driven with a main power source such as a hydraulic primary pump coupled with a combustion engine or directly with the combustion engine. Typically, one set of wheels are directly driven by the combustion engine or the hydraulic primary pump and the other set of wheels, typically the steerable wheels, are often equipped with hydraulic fluid motors for assisting in driving the vehicle. Accordingly, a four-wheel drive vehicle is provided for better performing in rough and slippery terrains such as muddy fields and construction sites.
The hydraulic fluid assist motors are typically used only when needed and, for that reason, a high pressure fluid valve is provided wherethrough the assist motors are selectively energized and de-energized. For example, the assist motors are energized when the vehicle is used in a construction or agricultural field, whereas they are de-energized when it is driven on paved surfaces, for example, from job site to job site.
A flow dividing valve is also typically provided in conjunction with or separate from the on/off valve. The flow dividing valve functions to regulate the flow of hydraulic fluid to the two assist motors and prevent the wheels driven by the assist motors from slipping. In this regard, the high pressure hydraulic fluid passes through the flow dividing valve to the assist motors and, thereafter, on the low pressure side the hydraulic fluid passes from the motors through flow divider valve and back to the hydraulic pump whereat the hydraulic fluid may again be increased in pressure and again delivered through the valve to the motors. Typically, the flow divider includes components for sensing the pressure of the hydraulic fluid being delivered to each of the assist motors and, in the event the pressure at one motor decreases, the components are adapted to shift in a manner whereby hydraulic fluid flow to the decreasing pressure side is decreased. This in turn increases hydraulic fluid flow to the other assist motor and thereby tends to equalize the pressure of the hydraulic fluid delivered to each of the assist motors. For example, in the event that a wheel driven by one assist motor experiences ice and slips, it will cause its assist motor to turn more rapidly and draw more hydraulic fluid. This translates to a hydraulic fluid pressure drop in that motor which in turn is sensed and corrected by the flow dividing valve.
Although on/off valves and flow dividing valves have been devised, manufactured and used extensively in the past, such valves have shortcomings and drawbacks. Flow dividing valves of the past have generally been costly to manufacture. More importantly, they experience substantial frictional losses in accomplishing their intended result and, therefore can be very inefficient. These frictional losses can also increase the temperature of the hydraulic fluid thereby requiring additional heat dissipating devices and otherwise affecting other system components.
Accordingly, a need exists for an on/off valve and flow dividing valve that can be manufactured relatively inexpensively and which accurately and efficiently divides the flow of hydraulic fluid to two hydraulic assist motors with relatively smaller frictional losses.